1. Field of the Invention:
The present invention relates to capacitors and is particularly directed to an axially-wound electrical capacitor, particularly a power capacitor.
2. Description of the Prior Art
Capacitors of the type set forth above are constructed of dielectric plastic layers (for example, polypropylene, polycarbonate, polyethyleneterephthalate and other suitable plastics) and have regenerably thin metal layers (for example of aluminum, zinc or alloys of aluminum and zinc) as electrodes that are either applied on the dielectric layers or on carrier layers (for example, paper) arranged in the field-free space. For contacting the electrodes arranged in an offset fashion, contact layers are produced on the end faces of the windings, for example in accordance with schoopage techniques.
If required, a plurality of capacitor windings can also be interconnected with one another.
Furthermore, certain types of capacitors have an impregnation with an insulating, dielectric fluid such as, for example, mineral oil and/or an electronegative gas such as, for example, sulphur hexafluoride.
Such capacitors, particularly the liquid-impregnated capacitors, are integrated in a metal housing.
It is already well known in the art to provide smaller, non-impregnated capacitors with a plastic envelope that provides, for example, enveloping with epoxy resin or extrusion-coating with thermoplastics or, respectively, thermosetting plastics.
In addition to other components, fully-insulated capacitors in an axial structure are required for wiring GTO thyristors.
When the capacitors are manufactured with a known structure having windings tightly assembled in metal housings, there is the possibility of subsequent, full insulation. To that end, for example, the housing can be integrally cast or, respectively, extrusion-coated, and the manufacture becomes involved and expensive as a result thereof.
Given the plastic envelope heretofore known only for small types of capacitors, the envelope material must be joined with adequate tightness in the region of the lead-through of the contacts. Despite the utilization of adhesion promoters and/or despite roughening, fully satisfactory results have not been achieved either in extrusion coating or in integral casting, particularly given thermal cycling.
Given liquid-impregnated capacitor windings, furthermore, an enveloping after the impregnation is not possible due to the parting agent effect of the impregnation fluid. The plastic envelopes known in the art likewise do not provide any measures for making a flow cross-section adequate for the impregnation agent available after the fabrication of the envelope.